Pure Virtual Functions as a prototype

   
#include <iostream>
using namespace std;
   
class number {
protected:
  int val;
public:
  void setval(int i) { val = i; }
   
  // show() is a pure virtual function
  virtual void show() = 0;
};
   
class hextype : public number {
public:
  void show() {
    cout << hex << val << "\n";
  }
};
   
class dectype : public number {
public:
  void show() {
    cout << val << "\n";
  }
};
   
class octtype : public number {
public:
  void show() {
    cout << oct << val << "\n";
  }
};
   
int main()
{
  dectype d;
  hextype h;
  octtype o;
   
  d.setval(20);
  d.show(); // displays 20 - decimal
   
  h.setval(20);
  h.show(); // displays 14 - hexadecimal
   
  o.setval(20);
  o.show();  // displays 24 - octal
   
  return 0;
}

1.	virtual function from base and derived classes
2.	Virtual function and two subclasses
3.	Abstract classes by virtual function with no body
4.	Override non-virtual function
5.	Implementing Pure Virtual Functions
6.	Illustration of the Use of Virtual Inheritance
7.	Using Virtual Methods
8.	Multiple Virtual Functions Called in Turn
9.	Virtual Copy Constructor
10.	virtual functions accessed from pointer
11.	virtual functions with person class
12.	Call parent virtual function
13.	Using Virtual Functions to control the behaviour
14.	Virtual Functions Are Hierarchical
15.	Virtual function in three level inheritance
16.	The Virtual Attribute Is Inherited
17.	Virtual Functions and Polymorphism
18.	A base class reference is used to access a virtual function
19.	Virtual base classes.
20.	virtual members

Pure Virtual Functions as a prototype : virtual function « Class « C++

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